This invention relates to the production of olefin polymers with a supported chromium oxide catalyst.
In the production of olefin polymers utilizing a solution process the production rate, that is, the pounds of polymer produced per unit of time per reactor, is limited by the viscosity of the polymerization medium. Thus, when the amount of polymer reaches a certain level, the viscosity of the polymer solution becomes too great to be handled by the filters and centrifuges. As a general proposition, the melt index of the polymer being produced varies with temperature, higher melt index (lower molecular weight) polymer being produced at the higher temperatures. Thus, this problem cannot be solved simply by raising the temperature since this produces a different polymer. Greater production rates could be obtained if polymer of a given melt index could be produced at a higher temperature since this would allow a greater concentration of polymer in the solution. It is further desirable to operate at a higher temperature so as to improve the efficiency of heat removal during the polymerization. Also higher reactor effluent temperature improves catalyst removal and solvent removal efficiency. Even in slurry polymerization processes where the melt index formed is inherently relatively low, there are applications for the resulting polymer such as high grade resin where an even lower melt index is needed.
Unfortunately, however, known additives for decreasing the melt index tend to reduce productivity, thus requiring a compromise between the desired melt index and high productivity.